1. Field of the Invention
The present invention relates to a sputtering apparatus for forming thin films on a semiconductor substrate such as silicon, or on a substrate of metal, glass, ceramics, plastics or the like, in vacuum in a manufacturing process of a semiconductor device or an electronic device, and to a method for controlling the sputtering apparatus.
2. Related Background Art
In modern semiconductor devices and electronic devices, a complex alloy, compound or mixture has come into use for a material playing a central role along with the improvement of device performance. For a thin film composed of such a material, there has been conventionally used a target and a deposition material of a similar composition to a desired thin-film material in a physical vapor deposition (PVD) method, such as a sputtering method and a vapor deposition method. However, the composition of the formed thin film often deviates from the composition of the target or the deposition material in the PVD method. Since the device characteristics of modern devices are extremely sensitive to the composition of those thin-film materials, there has been the need to discover a target or a deposition material whereby the desired composition can be obtained, if a compositional deviation occurs.
In order to seek for a new thin-film material, device characteristics are evaluated while varying the composition of a thin film. In such work, a vacuum apparatus is exposed to the atmosphere each time and a compositionally different target or deposition material is attached to the apparatus to perform film-forming. Thus, the work has required extra development costs and a prolonged period of time. In order to cut such development costs, the Journal of the Magnetics Society of Japan, Vol. 21, No. 4, pp. 505-508 (1997) discloses a method in which Pt pellets are attached to an Mn target to provide a target at the time of forming a Pt—Mn alloy thin film, and the composition of the thin film is adjusted by varying the number of Pt pellets. According to this method, there is no need to prepare a plurality of compositionally different Pt—Mn targets, it is possible to reduce development costs. In order to perform the work of attaching Pt pellets, however, the vacuum apparatus needs to be exposed to the atmosphere each time. The method therefore does not lead to the reduction of development time.
In contrast, as a sputtering method capable of making the composition adjustment of a target or a deposition material without the need for the atmospheric exposure of apparatus, there is a multi-target co-sputtering method in which a plurality of sputtering cathodes are discharged simultaneously. Japanese Patent Application Laid-Open No. 2005-256112 discloses a multi-target sputtering method using a double rotary shutter in which two shutters, each having two openings, are arranged one on top of the other, in order to perform two-target co-sputtering. In the method, desired two cathodes are selected with one shutter and open/close operations are performed with the other shutter, in order to shift from a pre-sputtering step to a full-scale sputtering step, thereby performing two-target co-sputtering. In a case where a Pt—Mn thin film is formed, it is possible to adjust the composition of the thin film by preparing a Pt target and an Mn target and varying power applied to each target. Accordingly, it is possible to significantly reduce the cost and time of developing compositionally different thin films.
In the method disclosed in Japanese Patent Application Laid-Open No. 2005-256112, however, the combination of targets, and the number of targets that can be sputtered simultaneously, have been limited since one shutter plate is fixed as a shutter for cathode selection and the other shutter plate is used for open/close operations. Specifically, only two targets can be sputtered simultaneously in a sputtering apparatus in which five targets are arranged.